The program that removed space debris in LEO that could harm the space elevator.

The Fountains of Paradise is a great example of Clarke's writing style; great difficulties accompany any great enterprise, but the calm application of the scientific method and sound engineering principles will always prevail.

For two hundred years, satellites of all shapes and sizes, from loose nuts and bolts to entire space villages, had been accumulating in Earth orbit. All that came below the extreme elevation of the Tower, at any time, now had to be accounted for, since they created a possible hazard. Three-quarters of this material was abandoned junk, much of it long forgotten. Now it had to be located, and somehow disposed of.

Fortunately, the old orbital forts were superbly equipped for this task. Their radars - designed to locate oncoming missles at extreme ranges with no advance warning - could easily pinpoint the debris of the early Space Age. Then their lasers vaporized the smaller satellites, while the larger ones were nudged into higher and harmless orbits.

Clarke isn't kidding about the problem of space debris; it has been a known problem since the sixties. Clarke had one possible solution; fortunately, no orbiting fortresses with lasers have been placed in orbit (as far as we know!). Take a look at Terminator Tether - Electrodynamic Tether Solution to Space Debris for a more modern solution.
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